A World to Explore

Another brachiopod this week. This simple fossil is an internal mold of the brachiopodPentamerus oblongus (J. de C. Sowerby, 1839). It was a very common and widespread taxon throughout North America and Europe in the Early Silurian. This particular specimen was found in a dolomite of the Clinton Group of New York State. This species has been an important fossil for reconstructing Early Silurian paleocommunities, and it is useful in biostratigraphy as well.

I chose this specimen because it has the preservation I have seen in almost every pentamerid brachiopod I have collected: it is an internal mold formed when sediment filled the calcitic shell, was cemented, and then the shell dissolved. We are looking at an impression of a sort of the interior surface of the brachiopod. The posterior (hinge region) of the brachiopod is at the top of this view. You can see a straight slit that represents the ventral muscle field complex (spondylium) that was part of the ventral valve. This was a kind of shelly septum on the floor of the brachiopod interior. we would not see this feature (or rather what is left of it) if the exterior shell had not been removed.The above is a drawing of Pentamerus oblongus as it looked with its original shell. In this view, unlike our specimen, we are looking at the dorsal valve with the ventral valve visible beneath it.The genus Pentamerus was named in 1813 by James Sowerby (1757-1822), a prolific scientist we met earlier with our specimen of the Cretaceous bivalve Inoceramus. The species Pentamerus oblongus was fittingly named by his eldest son, James de Carle Sowerby (1787-1871), in 1839. J. de C. Sowerby is shown above in his latter years. The younger Sowerby was an unusual combination of a paleontologist, botanist and mineralogist. He was a friend of the extraordinary scientist Michael Faraday (1791-1867), so he would have had encouragement to be an accomplished polymath. He is said to have conceived one of the first classification of minerals by their chemical compositions. In 1838, J. de C. Sowerby and his cousin Philip Barnes founded the Royal Botanic Society and Gardens (now part of Regent’s Park, London). On top of all this, he was a spectacular scientific illustrator. How many such diverse scientists do we have today?

References:

Johnson. M.E. 1977. Succession and replacement in the development of Silurian brachiopod populations. Lethaia 10: 83-93.

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor. We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student. We post abstracts of each study as they become available. The following was written by Richa Ekka, a senior geology major from Jamshedpur, India. She finished her thesis and graduated in December, so her work is the first of her class to be posted. You can see earlier blog posts from Richa’s study by clicking the Estonia tag to the right.

In July 2012, I travelled to Estonia with my advisor, Dr. Mark Wilson, a fellow Wooster geology major Jonah Novek, Dr. Bill Ausich and three geology students of The Ohio State University. It was quite an adventure with a few unexpected changes in our travel plans. Dr. Wilson and I had to spend a day in Tallinn, waiting for Jonah as his flight was delayed. Upon Jonah’s arrival we headed for the island of Saaremaa, where I carried out my research. We stayed in Kuressaare, on the southern shore of the island. I did my field research on the Soeginina Beds at Kübassaare in eastern Saaremaa.

The Kübessaare coastal area is an outcrop of the Soeginina Beds in the Paadla Formation (lowermost Ludlow) that represents a sequence of dolostones, marls, and stromatolites (see figure above). The Soeginina Beds represent rocks just above the Wenlock/Ludlow boundary, which is distinguished by a major disconformity that can be correlated to a regional regression on the paleocontinent of Baltica. The occurrence of these sedimentary structures and fauna in the Soeginina Beds provide us with evidence that there was a change in paleoenvironmental conditions from a shelfal marine environment to a restricted shallow marine setting followed by a hypersaline supratidal setting.

The base of the section has Chondrites trace fossils and marly shale that represent a shelfal marine environment. The next section on top has dolostones with Herrmannina ostracods, oncoids, and eurypterid fragments that indicate a shallow marine setting (lagoonal). The next section above has stromatolites (see figure below) that form in exposed intertidal mud flats. The topmost section has halite crystal molds that represent a hypersaline supratidal setting. Thus, we see a change from shelfal marine environment to a restricted shallow marine setting and finally to a hypersaline supratidal setting.

CHARLOTTE, NORTH CAROLINA–Matt Peppers (’13), a member of the intrepid Team Utah, presented his poster today at the 2012 Geological Society of America annual meeting. Matt is working on the dynamics of the volcanic flows in the Black Rock Desert. Here is his abstract.

The third Wooster presenter was Richa Ekka (’13), who worked on Saaremaa Island in Estonia this summer. Her abstract describing her project with a Silurian shallow water dolomitic sequence is here.

Once again it was a joy to watch our students interact with the many geologists who discussed their posters and projects. I now can’t imagine coming to these meetings without an enthusiastic group of our students.

CHARLOTTE, NORTH CAROLINA–The brave souls Jonah Novek (’13) above and Kit Price (’13) below were the first Wooster students to present their posters at the 2012 Geological Society of America meeting. Jonah worked in Estonia this past summer on Early Silurian recovery faunas in the Hilliste Formation on Hiiumaa Island. You can read his abstract directly here, and you can recall his field adventures by searching for “Jonah” in this blog. Kit collected Upper Ordovician cryptic sclerobiont fossils in Indiana in the late summer. Her abstract is here, and you can see her work in this blog by searching for “Kit“. Jonah and Kit started off our GSA presentation experience with confidence and joy.

During our Estonian expedition this summer, Richa Ekka (’13) chose as her Independent Study project focus the Soeginina Beds (lowermost Ludlow, Upper Silurian) of the Paadla Formation exposed in southeastern Saaremaa Island. These carbonate sediments, mostly dolomitized, were deposited in very shallow conditions — so shallow that in some places we have syneresis cracks and halite crystal molds. I expected the fossils to be mostly stromatolites and rare traces. We were pleasantly surprised to also find, though, a bed with numerous valves of the giant ostracod Herrmannina Kegel 1933 (shown above). I should have guessed that the hardy and extraordinarily successful ostracods would have been present.

At first we thought that these slightly-recrystallized shells must be bivalves (clams) because of their relatively large size (up to 25 mm long). But we didn’t see the typical bivalve muscle scars or hinging teeth and sockets. They had to be ostracods — but so big? The typical ostracod valve, shown below, is two mm or less in length. These Silurian examples are over 10 times that size. It would be like me meeting my 60-foot equivalent. Turns out that Herrmannina is known for its gigantism in the ostracod world — and it is not even the largest.

Cyamocytheridea sp. from the Eocene of Nederokkerzeel, Belgium. (Public Domain, Wikimedia.) This is the typical small size for an ostracod.Today the ostracods, members of the Phylum Arthropoda, have over 8000 living species in both fresh and marine waters. Most crawl or burrow into sediments (that is, most are vagrant benthic epifaunal and infaunal), and a few are suspended in the water column (planktic). They have a wide range of feeding habits, from filter-feeding and deposit-feeding to herbivory and carnivory. (This is a key to their survival from the Early Paleozoic to today.) The living ostracod above shows that they are essentially a large head with several pairs of appendages inside two hinged valves. (The image is public domain from Anna33 at Wikipedia.) Their sex life is astonishing: ostracods have the largest sperm of any animals in both relative and absolute measures. Ostracod sperm are often ten times the length of the male body. (No, I don’t know how that works!)

Herrmannina is in the Order Leperditicopida of the Class Ostracoda. This genus was named in 1933 by Wilhelm Kegel (1890-1971), a geologist in the Preussische Geologische Landesanstalt of Berlin, Germany, who specialized in the Devonian and Carboniferous systems. I couldn’t find out much more about Dr. Kegel, but did stumble across an uncredited, undated low-resolution photo of him above. A fuzzy face from our paleontological past!

Kesling, R.V. 1958. A new and unusual species of the ostracod genus Herrmannina from the Middle Silurian Hendricks Dolomite of Michigan. Contributions, Museum of Paleontology, The University of Michigan 14, No. 9: 143-148.

This week’s fossil is a tiny little crinoid with an odd shape. Calceocrinus balticensis (shown above with the scale bar as one millimeter) is a new species from the Lower Silurian (Llandovery) of Hiiumaa, western Estonia. It is part of a series of new crinoid taxa described in the most recent issue of Acta Palaeontologica Polonica by Ausich et al. (2012). All that geological work in Estonia by Ohio State and Wooster geologists is resulting in several paleontological publications, all with the collaboration of our friend Olev Vinn at the University of Tartu, Estonia.

The western Estonian island of Hiiumaa where our little crinoid was found. (Image courtesy of Google Maps.)

Calceocrinus balticensis Ausich, Wilson and Vinn, 2012 (to give its full and glorious name) is unusual because its crown (the filter-feeding “head” of the crinoid) is recumbent on the column (the “stem”). In the images above you can see the column as a series of disks on their sides at the bottom of the view. The crown is the set of larger plates attached to the top of the column, from which there are several arms extending to the right. This new species is the first of its genus from the paleocontinent Baltica. It had sister species in North America on what became Anticosti Island in eastern Canada (see Ausich and Copper, 2010).

Calceocrinids (Order Calceocrinida Ausich, 1998) lived very close to the seafloor. The column of an individual, which in other crinoids holds the crown far off the substrate, lay horizontally along the bottom. The crown was hinged at its base so that it could be elevated perpendicular to the stem with the arms spread wide to filter organic material from the water. During non-feeding times the crown would lie inconspicuous on the bottom. This crinoid literally had a very low profile compared to its showy cousins.

Now, though, the shy little Calceocrinus balticensis gets a moment of exposure and formal admission to the roll call of life’s species.

There are two common fossil types that begin with “strom” and look roughly alike to the untrained eye. One is the stromatoporoid, which is a calcareous sponge, and the other is the stromatolite, which is a layered structure produced by photosynthetic bacteria. I hadn’t seen them together until our expedition to the Silurian of Estonia last summer. Wooster senior Nick Fedorchuk (’12) collected the specimen above at his outcrop of limestones and dolomites just above the Wenlock/Ludlow Boundary along Soeginina Cliff, Saaremaa. (In the rock sequence Richa Ekka is now studying.) We thought it was simply a stromatolite until he cut it to show that the base was a stromatoporoid.“Stroma” is Greek for a bed or layer. Both stromatolites and stromatoporoids have horizontally laminated structures. The “lite” in stromatolite means rock, so a stromatolite is literally a “layered rock”. They are accretionary structures made by mostly cyanobacteria that collect and bind fine sediment into thin layers, usually in very shallow waters. Often the bacteria make their own calcareous cement for these laminae as a byproduct of photosynthesis. They’ve been doing this for a long time: the earliest known fossils are 3.5 billion-year-old stromatolites.

Stromatoporoids are very different. The “poroid” refers to their semi-porous skeletal layers, which are separated from each other by minuscule pillars. Their peak of abundance was in the Silurian and Devonian Periods, but they survived all the way up into the Cretaceous. They made significant reefs in the Paleozoic, often more common than the corals back then. We believe that they were a type of sponge (Phylum Porifera) with a thin layer of soft tissue on the exterior layer filter-feeding in the typical sponge manner.

Stromatolites are more common in sediments formed in very shallow, warm marine waters with elevated salinity; stromatoporoids liked more normal marine conditions. Finding the stromatolite on top of the stromatoporoid here means that either the environment changed between the two (shallowing, likely), or that the stromatoporoid was dislodged from more offshore waters during a storm and washed into a shallow lagoon, becoming a substrate for stromatolitic growth.

Curiously, there was a suggestion in 1990 by Kaźmierczak and Kempe that stromatoporoids ARE stromatolites. They pointed out that precipitation features in modern stromatolites can be very complex, producing features that resemble those of ancient stromatoporoids. This idea gained no traction, though, and most paleontologists are satisfied that these two types of “strom” have very different origins.

Editor’s note: The Wooster Geologists in Estonia this summer wrote abstracts for posters at the Geological Society of America Annual Meeting in Charlotte, North Carolina, this November. The following is from student guest blogger Jonah Novek in the format required for GSA abstracts:

Analysis of a Rhuddanian (Llandovery, Lower Silurian) sclerobiont community in the Hilliste Formation on Hiiumaa Island, Estonia: a hard substrate-dwelling recovery fauna

The Hilliste Formation on the island of Hiiumaa, western Estonia, is a Rhuddanian (Llandovery, Lower Silurian) sequence of limestones and shales. It represents some of the earliest Silurian rocks on the paleocontinent of Baltica. The depositional system was tropical and shallow marine with tempestites indicated by overturned and broken corals and stromatoporoids. This unit contains a recovery fauna from the Ordovician Mass Extinction. Major taxa in the Hilliste Formation include crinoids, trilobites, bryozoans, corals, stromatoporoids, gastropods, and brachiopods. Sclerobiont communities (organisms that lived on or within hard substrates) have not yet been described from Rhuddanian faunas. The Hilliste Formation contains many encrusters and a few borings on skeletal substrates (primarily corals and crinoid stems). These sclerobionts include at least three kinds of crinoid holdfasts, cornulitids, sheet-like bryozoans, runner-type bryozoans, erect bryozoan holdfasts, and auloporid corals. Most if not all of these sclerobionts inhabited dead substrates. We studied the Hilliste Formation in a small quarry near the village of Hilliste on Hiiumaa. Numerous encrusted and bored specimens were collected for analysis of sclerobiont occurrences in this rare example of a Rhuddanian hard substrate community. These encrusters and borings, along with the macrofauna, have a distinct Late Ordovician aspect.

The Soeginina Beds in the Paadla Formation on the island of Saaremaa, western Estonia, are a Lower Ludlow (Upper Silurian) sequence of dolostones, marls, and stromatolites. They represent rocks just above the Wenlock/Ludlow boundary, which is distinguished by a major disconformity that can be correlated to a regional regression on the paleocontinent of Baltica. We interpret the depositional environment of the Soeginina Beds as having been a hypersaline lagoon. Our evidence includes halite crystal molds, oscillation ripples, eurypterid fragments, stromatolites, ostracods, gastropods, Chondrites trace fossils, intraclasts and oncoids. Nautiloid conchs are common, probably because storm currents washed them in. We measured two sections of the Soeginina Beds at Kübassaare, eastern Saaremaa, western Estonia. The beds in one section are virtually horizontal; in the second they are steeply dipping, probably because of Pleistocene glacial ice overpressure. The beds begin with fine-grained dolostone and end with large, well-preserved domical stromatolites. The equivalent section at Soeginina Pank in western Saaremaa (about 86 kilometers away) has larger oncoids, branching coral fragments, and smaller stromatolites. It is also more heavily dolomitized. We interpret these differences as showing the western Soeginina Beds were deposited in slightly deeper, less saline waters than those in the east at Kübassaare.

TALLINN, ESTONIA–This morning Bill Ausich and I examined fossils in the collections of the Institute of Geology at Tallinn University of Technology (the cool exterior of which is shown above). The Chief Curator, Ursula Toom, generously came in from her vacation to show us some important Ordovician and Silurian crinoid specimens, as well as assemblages from the Lower Silurian throughout Estonia. We had an excellent time looking at gorgeous fossils in a classic museum. (We were here in 2009 with Rob McConnell and Palmer Shonk as well.)

It must be an interesting place if they bolt a rock up off the ground in front!

Bill is here looking at crinoids Ursula set aside for us to examine. Note his use of an iPad for taking notes and images, just like Wooster geologists did last year at Ohio State. Bill carries his entire pdf library with him on his iPad, and makes many annotated images of museum specimens.

Typical hall of cabinets in the Institute of Geology. Each set of drawers is on a mechanical device for closing the aisles to increase storage space.

This is a row of cabinets with one drawer opened. Note the use of a drawer partially opened underneath for support. (A rough experience once before I learned this trick …)

A typical drawer of specimens. These are newly collected from the Reinu Quarry by our friend and colleague Olev Vinn.

A specimen label. Unfortunately some are nearly indecipherable. Sometimes it is because a Russian worker was transliterating information into Latin letters. There is often an interesting mix between the Russian, Estonian and English languages. Fortunately Ursula and others can quickly translate for us!

We enjoyed working in the Institute of Geology collections very much. They are not only superbly organized, much of their content is listed (and even imaged) online. We saw many critical specimens, and Bill was able to borrow some important crinoids. Thank you to Ursula for her kindness and excellent assistance!